Class SymbolTable

java.lang.Object
  SymbolTable

Direct Known Subclasses:

CgenClassTable

class SymbolTable

extends java.lang.Object

Implements the symbol table data abstraction.

In addition to strings, compilers must also determine and manage the scope of program names. A symbol table is a data structure for managing scope. Conceptually, a symbol table is just another lookup table. The key is the symbol (the name) and the result is whatever information has been associated with that symbol (e.g., the symbol's type).

In addition to adding and removing symbols, symbol tables also support operations for entering and exiting scopes and for checking whether an identifier is already defined in the current scope. The lookup operation must also observe the scoping rules of the language; if there are multiple definitions of identifier x, the scoping rules determine which definition a lookup of x returns. In most languages, including Cool, inner definitions hide outer definitions. Thus, a lookup on x returns the definition of x from the innermost scope with a definition of x.

Cool symbol tables are implemented using Java hashtables. Each hashtable represents a scope and associates a symbol with some data. The ``data'' is whatever data the programmer wishes to associate with each identifier. An example illustrating the use of symbol tables is in the file SymtabExample.java.

See Also:

AbstractSymbol, SymtabExample

Field Summary

private java.util.Stack

tbl

Constructor Summary

SymbolTable()
Creates an empty symbol table.

Method Summary

void	addId(AbstractSymbol id, java.lang.Object info) Adds a new entry to the symbol table.
void	enterScope() Enters a new scope.
void	exitScope() Exits the most recently entered scope.
java.lang.Object	lookup(AbstractSymbol sym) Looks up an item through all scopes of the symbol table.
java.lang.Object	probe(AbstractSymbol sym) Probes the symbol table.
java.lang.String	toString() Gets the string representation of the symbol table.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

tbl

private java.util.Stack tbl

Constructor Detail

SymbolTable

public SymbolTable()

Creates an empty symbol table.

Method Detail

enterScope

public void enterScope()

Enters a new scope. A scope must be entered before anything can be added to the table.

exitScope

public void exitScope()

Exits the most recently entered scope.

addId

public void addId(AbstractSymbol id,
                  java.lang.Object info)

Adds a new entry to the symbol table.

Parameters:

id - the symbol

info - the data asosciated with id

lookup

public java.lang.Object lookup(AbstractSymbol sym)

Looks up an item through all scopes of the symbol table. If found it returns the associated information field, if not it returns null.

Parameters:

sym - the symbol

Returns:

the info associated with sym, or null if not found

probe

public java.lang.Object probe(AbstractSymbol sym)

Probes the symbol table. Check the top scope (only) for the symbol sym. If found, return the information field. If not return null.

Parameters:

sym - the symbol

Returns:

the info associated with sym, or null if not found

toString

public java.lang.String toString()

Gets the string representation of the symbol table.

Returns:

the string rep